Martes Foot-Loading and Snowfall Patterns in Eastern North America

Abstract

American martens (Martes americana) and fishers (M. pennanti) require large areas and live in complex, interacting communities of medium and large size carnivores. Nevertheless, habitat studies of these species continue to emphasize mid-to fine-scale habitat relationships, and rarely examine interspecific relations. Based on our data on foot-loading (ratio of body mass to total foot area) for fishers and martens, and snowfall patterns across eastern north america, we conclude that broader-scale habitat and interspecific relations of these 2 species may affect their regional distributions. Although foot-loading was influenced by sex (P<0.001) and age (P=0.08), foot-loading in fishers was >2 times greater (P<0.001) than martens across all of the 4 age-sex classes. Relative to other large- and medium-sized carnivores in the forests of eastern North America, the 2 Martes species have the shortest legs, and thus are most dependent on low foot-loading for mobility in soft snow. To assess temporal and spatial variation in snowfall as related to potential Martes distributions, we used a snowfall threshold reported for maine to define the mid-point of a zone with overlapping populations of fishers and martens and applied this threshold (240 cm mean annual snow) to regional snowfall data for 1970–90. Regression analyses of weather data in conjunction with data on latitude, longitude, and elevation were used to model mean annual snowfall. Since the late 1700’s, there has been a general warming trend across eastern North America. If previously proposed hypotheses that snow limits fishers, and large populations of fishers limit martens are true, then one would predict that martens historically occurred south of where they do today. Further, if snowfall continues to decline in the region, fisher populations may expand and martens may decline. To test these predicted broad-scale distribution patterns, we suggest that past and modern occurrence data for fishers, martens, and other forest carnivores be examined across the historic range of both species to evaluate the hypothesis that interactions among morphology and climate affect distribution and degree of sympatry in North American Martes.